How to play reverse animation?

Hi I want to play reverse animation. ie Move a cube from point A to B and then back from B to A I have tried using links http://answers.unity3d.com/questions/466197/how-to-play-animation-in-reverse.html http://forum.unity3d.com/threads/playing-animation-backwards.15071/

but every time it throws error

Script using is

 using UnityEngine;
 using System.Collections;
 
 public class test : MonoBehaviour {
     public GameObject cube;
 
     Animator animator;
     // Use this for initialization
     void Start () {
         animator = cube.GetComponent<Animator>();
     }
     
     // Update is called once per frame
     void Update () {
         if(Input.GetKey(KeyCode.RightArrow)) {
             animator.SetTrigger("move");
         }if(Input.GetKey(KeyCode.LeftArrow)) {
             animator.animation["@anim"].speed = -1;
             animator.SetTrigger("move");
         }
     }
 }

Thanks...

Did you even read the question ? before closing it you fool....? I know what is null pointer exception is...@SaraCecilia